Introduction to Programming and Java. 2 The Central Processing Unit The speed of a CPU is controlled by the system clock which generates an electronic.

Introduction to Programming

and Java

2

The Central Processing Unit

• The speed of a CPU is controlled by the system clock which generates an electronic pulse at regular intervals

• One “machine cycle” per pulse which performs a part of a machine language command, for example

• move info in register A to memory location 58467

• add contents of register A to register B

• Computers generate billions of pulses per second

• What’s a machine language command?

Machine Language Commands

• A machine language command is the most basic command stored in a computer’s memory.

• For example: – 10110000 01100001

• A machine language program is a sequence of hundreds of such commands.

• Sound like fun?• Early computer programmers

didn’t like dealing with machine language so they invented assembly language.

Assembly Language Commands

• A single assembly language command corresponds to a single machine language command but is easier for a programmer to read/write/understand

• For example– move #061,1207

• A assembly language program is a sequence of hundreds of such commands.

• Sound like fun? • It’s better, but early computer

programmers didn’t like dealing with assembly language much either so they invented high level language.

finit

mov cx,8

mov al,[Y]

or al,al

jnz LoadX

fld1

jmp Exit

LoadX:

fld [X]

fld [X]

dec cx

shl al,1

High Level Language Commands

• A high level language command can correspond to several assembly language commands

• High level languages also allow programmers to use “names” instead of memory addresses

• For example:

cost = (price – discount) * (1 + taxrate);• A high level language program is a

sequence of many such commands.• Sound like fun?• Yes!!!!!!!!!!!!!!!!

Grace Hopper

6

8086 CPU

Program Translation I

• Each type of CPU executes only a particular machine language

• A high level language program must be translated into machine language before it can be executed

• A compiler is a software tool which translates source code into a specific target language

high level source code

Compiler

8086 machinecode

7

8086 CPU

Program Translation 2

• Each type of CPU executes only a particular machine language

• A high level language program must be translated into machine language before it can be executed

• A interpreter is a software tool which translates source code into a specific target language one line at a time, as needed

high level source code

Interpreter

8

High Level Languages

• There are hundreds of different high level languages

• Each has its strengths and weaknesses

• We’ll use Java in this course• And there are even “higher”

level languages called 4th generation languages

Java

• A programming language specifies the words and symbols that we can use to write a program

• A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements

• The Java programming language was created by Sun Microsystems, Inc.

• It was introduced in 1995 and it's popularity has grown quickly since

Java Program Structure

• In the Java programming language:– A program is made up of one or more classes– A class contains one or more methods– A method contains program statements

• These terms will be explored in detail throughout the course

• A Java application always contains a method called main

• See Lincoln.java (page 29)

11

Java Program Structure

public class MyProgram

{

}

// comments about the class

class header

class body

Comments can be placed almost anywhere

12

Java Program Structure

public class MyProgram

{

}

// comments about the class

public static void main (String[] args)

{

}

// comments about the method

method headermethod body

13

Comments

• Comments in a program are called inline documentation

• They should be included to explain the purpose of the program and describe processing steps

• They do not affect how a program works

• Java comments can take three forms:

// this comment runs to the end of the line

/* this comment runs to the terminating symbol, even across line breaks */

/** this is a javadoc comment */

14

Identifiers

• Identifiers are the words a programmer uses in a program

• An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign

• Identifiers cannot begin with a digit

• Java is case sensitive - Total, total, and TOTAL are different identifiers

• By convention, programmers use different case styles for different types of identifiers, such as

– title case for class names - Lincoln

– upper case for constants - MAXIMUM

Identifiers

• Sometimes we choose identifiers ourselves when writing a program (such as Lincoln)

• Sometimes we are using another programmer's code, so we use the identifiers that he or she chose (such as println)

• Often we use special identifiers called reserved words that already have a predefined meaning in the language

• A reserved word cannot be used in any other way

16

Java Reserved Words

abstractassertbooleanbreakbytecasecatchcharclassconstcontinuedefaultdodouble

elseenumextendsfalsefinalfinallyfloatforgotoifimplementsimportinstanceofint

interfacelongnativenewnullpackageprivateprotectedpublicreturnshortstaticstrictfpsuper

switchsynchronizedthisthrowthrowstransienttruetryvoidvolatilewhile

17

White Space

• Spaces, blank lines, and tabs are called white space

• White space is used to separate words and symbols in a program

• Extra white space is ignored

• A valid Java program can be formatted many ways

• Programs should be formatted to enhance readability, using consistent indentation

• See Lincoln2.java

• See Lincoln3.java

Fall 2010 --- Do Lab Here

18

Java Translation

• The Java compiler (javac) translates Java source code into a special representation called bytecode

• Java bytecode is not the machine language for any traditional CPU

• Another software tool (java), called an interpreter, translates bytecode into machine language and executes it

• Therefore the Java compiler is not tied to any particular machine

• Java is considered to be architecture-neutral

19

Java Translation

Java sourcecode

Machinecode

Javabytecode

Bytecodeinterpreter

(java)

Bytecodecompiler

Javacompiler(javac)

Program Development

• The mechanics of developing a program include several activities

– understanding what the program is supposed to do

– designing the program

– writing the program in a specific programming language (such as Java)

– translating the program into a form that the computer can execute

– investigating and fixing various types of errors that can occur

• Computer programmers didn’t like dealing with all of this at the “command line” level, so they invented software tools that can be used to help with many parts of this process

Development Environments• There are many programs that support the development of Java

software, including:

– Sun Java Development Kit (JDK)– Sun NetBeans– IBM Eclipse– Borland JBuilder– MetroWerks CodeWarrior– BlueJ– jGRASP

• Though the details of these environments differ, the basic compilation and execution process is essentially the same

22

Syntax and Semantics• The syntax rules of a language define how we can put together

symbols, reserved words, and identifiers to make a valid program

sum = value1 + value2; // correct syntax

product = (value1)(value2); // incorrect syntax

• The semantics of a program statement define what that statement means (its purpose or role in a program)

• A program that is syntactically correct is not necessarily logically (semantically) correct

sum = value1 - value2; // logic error?

• A program will always do what we tell it to do, not what we meant to tell it to do

23

Errors

• A program can have three types of errors

• The compiler will find syntax errors and other basic problems (compile-time errors)

– If compile-time errors exist, an executable version of the program is not created

• A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)

• A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)

Basic Program Development

errors

errors

Edit andsave program

Compile program

Execute program andevaluate results

Problem Solving

• The purpose of writing a program is to solve a problem

• Solving a problem consists of multiple activities:

– Understand the problem

– Design a solution

– Consider alternatives and refine the solution

– Implement the solution

– Test the solution

• These activities are not purely linear – they overlap and interact

Problem Solving• The key to designing a solution is breaking it down into manageable

pieces

• When writing software, we design separate pieces that are responsible for certain parts of the solution

• An object-oriented approach lends itself to this kind of solution decomposition

• We will dissect our solutions into pieces called classes and objects

• An application/program can use

– the primitive Java language

– the Java library classes and objects (and their methods)

– “homemade” classes and objects (and their methods)

An example using (mostly) the primitive language

//*********************************************************// Sum01.java Author: Joyce//// Demonstrates a simple Java application.//*********************************************************

public class Sum01{ public static void main (String[] args) { int value1, value2; int sum; value1 = 7; value2 = 4; sum = value1 + value2;

System.out.println ("The sum of " + value1 + " and " + value2 + " is " + sum); }}

Java Library Classes

• Java 2 Platform Standard Edition 5.0

• The API Specification (see link off Joyce’s CSC 1051 page)

• There are almost 3,000 classes

• Packages/Sub-packages are for organizational purposes, for example

– awt: abstract windowing toolkit

– lang: fundamental to the Java language

Static Methods

• can be called directly through the class• not the “common” approach .. but the

easiest to understand• for example, all the methods of the Math

class are static:– abs– pow– sqrt– …

An example using some

static methodsfrom the Javalibrary Math

class

//*********************************************************// MathDemo.java Author: Joyce//// Demonstrates using static methods.//*********************************************************

public class MathDemo{ public static void main (String[] args) { int value1, value2; int sum; value1 = 7; value2 = 4; sum = value1 + value2;

System.out.println (value2 + " raised to the " + value1 + " power is " + Math.pow(value2, value1));

System.out.println ("The square root of the sum of " + value1 + " and " + value2 + " is " + Math.sqrt(sum)); }}

static method call

static method call

© 2007 Pearson Addison-Wesley. All rights reserved 2-31

Object-Oriented Programming

• Java is an object-oriented programming language

• As the term implies, an object is a fundamental entity in a Java program

• Objects can be used effectively to represent real-world entities (among other things)

• For instance, an object might represent a specific person’s bank account

• Each bank account object handles the processing and data management related to that account

© 2007 Pearson Addison-Wesley. All rights reserved 2-32

Objects

• An object has:

– state - descriptive characteristics

– behaviors - what it can do (or what can be done to it)

• The state of a bank account includes its account number and its current balance

• The behaviors associated with a bank account include the ability to make deposits and withdrawals

• Note that the behavior of an object might change its state

• Note that the state of an object might affect its behaviour

© 2007 Pearson Addison-Wesley. All rights reserved 2-33

Classes and Objects

• An object is defined by a class

• A class is the blueprint of an object

– Typically state is maintained in a set of private variables

– Typically public methods define the behaviors of the object

• A class represents a concept, and an object represents the embodiment of that concept

• Multiple objects can be created from the same class

© 2007 Pearson Addison-Wesley. All rights reserved 2-34

Objects and Classes

Bank Account

private double balance

public double deposit (double amount)

A class(the concept)

John’s Bank Accountbalance: $5,257

objects(the realization)

Bill’s Bank Accountbalance: $1,245,069

Mary’s Bank Accountbalance: $16,833

{ Account acct1 = new Account ("Ted Murphy", 72354, 102.56); Account acct2 = new Account ("Jane Smith", 69713, 40.00); Account acct3 = new Account ("Edward Demsey", 93757, 759.32);

acct1.deposit (25.85);

double smithBalance = acct2.deposit (500.00); System.out.println ("Smith balance after deposit: " + smithBalance);

System.out.println ("Smith balance after withdrawal: " + acct2.withdraw (430.75, 1.50));

acct1.addInterest(); acct2.addInterest(); acct3.addInterest();

System.out.println (); System.out.println (acct1); System.out.println (acct2); System.out.println (acct3); }

public class Experiment04{ public static void main (String[] args) { ... PairOfDice dice1 = new PairOfDice(); PairOfDice dice2 = new PairOfDice(); NumberStats stats1 = new NumberStats(); NumberStats stats2 = new NumberStats();

Scanner scan= new Scanner (System.in); DecimalFormat fmt= new DecimalFormat ("0.###");

System.out.print("See result of each dice roll? (Y = Yes) > "); boolean trace = scan.nextLine().equalsIgnoreCase("Y"); ... System.out.println("\nDice 1: " + dice1.maxString()); ... dice2 = new PairOfDice(numSides1, numSides2); stats1.submit(dice1.roll());...

object creation

object use

Inheritance• One class can be used to derive another via inheritance

• Classes can be organized into hierarchies

Bank Account

Account

Charge Account

Savings Account

Checking Account